Indian wildcard Yuki Bhambri delighted home fans with a 6-4, 6-3 win over Pablo Carreno Busta, who had been voted the ATP's most improved player for 2013 after jumping 650 places in the rankings.
The Spaniard, ranked 64 against Bhambri's 195, was unable to settle down against the Indian's aggressive play and went out in his first appearance in the tournament.
Bhambri, who faces third seed Fabio Fognini of Italy in the second round, said he looked forward to playing the tougher opponent.
"Hopefully I can take the confidence from this victory into my next match," the Indian number two said. "He will probably be rusty and I will try to take advantage of that."
Fognini, recovering from a leg strain, withdrew from the doubles where he was to partner with Indian veteran Leander Paes. But he is expected to be fit for the singles match.
Chennai-based Ramkumar Ramanathan, playing his maiden ATP Tour match, gave local fans another reason to celebrate when he came from behind to stun better-known compatriot and India's top player Somdev Devvarman 4-6, 6-3, 6-4.
Eighth seed Roberto Bautista Agut of Spain dropped by the wayside as unheralded players stepped up their game on the second day of the $450,000 ATP Chennai Open on Tuesday.
Agut, ranked 58th in the world, was stunned by Russian qualifier Alexander Kudryavtsev 6-4, 3-6, 6-3 in a match marked by baseline rallies at the Nungambakkam Tennis Centre.
"It was a hard match for me," the Spaniard admitted. "He is a player who runs for every ball and hits the ball very hard. I was not able to play like I wanted to."
Kudryavtsev's second round opponent will be Aljaz Bedene of Slovenia, who fought off a spirited challenge from Swiss qualifer Henri Laaksonen before winning 6-3, 5-7, 7-6 (7/0).
Seventh seed Edouard Roger-Vasselin of France qualified for a second-round clash against Jiri Vesely of the Czech Republic with a 6-1, 6-3 win over Spaniard Albert Ramos.
"It was very hot and humid out there and that made it tough for me as the match went on," the 30-year-old Frenchman said. "I am just glad it did not go into a third set."
The top four seeds -- Stanislas Wawrinka, Mikhail Youzhny, Fognini and Benoit Paire -- will be seen in action from Wednesday after being handed first-round byes.
Benjamin Becker of Germany, who was leading 6-4, 2-1 when his opponent Julian Reiser pulled out with stomach cramps, will play Wawrinka for a place in the quarter-finals.